The present invention pertains generally to medical monitoring methods and devices for analyzing and displaying electrophysiologic signals, and more particularly to systems and methods for connecting and disconnecting electrophysiologic signals detected at electrodes placed on a subject to and from detection amplifiers employed in such a medical monitoring device.
Medical monitoring involves monitoring the body of a subject to determine the state of health of the subject and to detect, identify, and diagnosis changes or abnormalities in the state of the body which may be indicative of problems, or for treatment evaluation. Medical monitoring may involve, for example, the motion of a subject""s body, temperature or chemical changes of the subject""s body, and/or audible or electrical signals reflected or generated by the subject""s body. For example, electroencephalography (EEG) is a form of medical monitoring wherein the electrical potentials of the subject""s brain are monitored by attaching electrodes to the subject""s scalp. In electromyography (EMG), electrical activity generated in the subject""s muscles is monitored using surface and/or needle recording electrodes. Medical monitoring may take place when a subject is at rest, in motion, or during the performance of a medical procedure. In some cases, medical monitoring involves monitoring the response of a subject to a stimulus. For example, evoked potential (EP) monitoring may be used to detect the electrical response of a subject""s nervous system to audible, visual, or electrical stimuli. Medical monitoring involving stimulus and response detection may be used in combination with EMG and various other medical monitoring methods as well.
Monitoring of the various physiologic signals generated by a subject""s body is typically performed using dedicated devices and/or systems. For example, EEG monitoring may be performed using a dedicated EEG monitoring system, by attaching electrodes to a subject to detect the electrical potential of the subject""s brain, amplifying and filtering the signals received from the electrodes for the desired frequency range of interest for EEG analysis, and providing the amplified and filtered signals to an EEG analysis system including software for further manipulating the EEG signals for analysis and display on an EEG system monitor. Similarly, EMG monitoring may be performed using a dedicated EMG monitoring system, by placing electrodes on the subject to detect electrical activity generated in the subject""s muscles, amplifying and filtering the signals detected by the electrodes for the desired frequency range of interest for EMG signals, and providing the amplified and filtered signals to an EMG analysis system including software for further manipulating the EMG signals for analysis and display on an EMG system monitor. Other signals of interest, e.g., vital signs, may be monitored in a similar manner, with a separate dedicated system provided for each type or modality of monitored signal of interest. Each such dedicated monitoring system may include or be connected to a system for providing stimulus to a subject, and for analyzing the particular detected signal of interest in response to the stimulus provided.
U.S. patent application Ser. No. 09/295,167, entitled xe2x80x9cMedical Signal Monitoring and Displayxe2x80x9d, by Wim Van Drongelen, and assigned to the assignee of the present application, describes a medical signal monitoring system and method providing the capability for an operator of the system to display and analyze physiologic signals of various types, frequencies, and modalities. Such a system may be provided with data from various physiologic signal acquisition systems, including systems for acquiring electrophysiologic signals from electrodes positioned on the subject. The system may further be connected to auditory, visual, and/or electrical stimulator systems, for controlling the providing of stimulation to a subject, while analyzing the physiologic signals received in response to the stimulus provided. Such a system includes an operator-friendly user interface which allows an operator of the system to designate and control, display, and analyze the physiologic signals received by the system and stimulus provided thereby. Such an integrated system provides a full range of diagnostic capability in a single device for use in a doctor""s office, operating room, intensive care unit, or emergency department.
In a typical application of a medical signal monitoring system, a plurality of electrodes may be attached to the body of a subject. Electrophysiologic signals, picked up by the electrodes, are carried by leads to a signal amplifier which may be part of or separate from the medical monitoring system. Typically, the signal provided on each such lead is amplified by a separate amplifier. The amplified signals may, for example, be filtered, digitized, and provided to the medical monitoring system for analysis and display. In this manner, several electrophysiologic signals, e.g., EEG and EMG signals, produced by a subject may be monitored continuously or periodically.
At times, it may be desirable to determine a subject""s response to an electrical signal applied to the subject (e.g., transcranial electric stimulation). A strong (high voltage) electrical signal applied to a subject""s body will be picked up by electrodes placed on the subject for detecting electrophysiologic signals. The stimulation signal will typically be much larger than any electrophysiologic signal produced by the subject""s body, especially in the area near where the electrical stimulation is provided. Thus, the electrical stimulation will tend to saturate the amplifiers which are connected by leads to electrodes placed on the subject near the point of electrical stimulation. Such over-saturation prevents recording of the response to the stimulation and may damage the amplifiers. Thus, to protect the amplifiers from damage, electrodes attached to a subject""s body near the point of electrical stimulation (and which are not used for monitoring the subject""s response to the stimulation) are typically physically removed from the subject before the electrical stimulation is provided to the subject. This situation is typical for a multi-modality monitoring device. By disconnecting selected electrodes from a subject, responses occurring at other electrodes can be recorded and potential damage to the amplifier is prevented. After the electrical stimulation is provided, these electrodes must be reattached to the subject if monitoring of the desired electrophysiologic signals is to continue. Thus, in a situation where it is desired to continually monitor certain physiologic signals, while periodically performing tests involving the application of electrical signals to a subject, it may be necessary to repeatedly physically remove electrodes from a subject (or remove the amplifier inputs), before electrical stimulation, and reattach the electrodes to the subject (or reattach the amplifier inputs), after stimulation is completed. This process is obviously time-consuming, and prone to error, as each time an electrode is removed from a subject there is the possibility that the electrode will not be placed back in the proper position on the subject (or reattached to the correct amplifier input).
What is desired, therefore, is a system and method for easily and quickly disconnecting electrophysiologic signals provided from electrodes attached to a subject from the amplifiers to which such signals are provided, when desired, such as before applying an electrical stimulation signal to the subject, and for easily and quickly reconnecting the electrophysiologic signals to the amplifiers after electrical stimulation is complete. Preferably, such a system and method provides for disconnecting electrophysiologic signals from the amplifiers without physically removing the electrodes from a subject or physically removing electrode leads from an amplifier input.
The present invention provides a system and method for easily and rapidly disconnecting medical signal monitoring electrodes from and connecting such electrodes to amplifiers in a medical signal monitoring system. In accordance with the present invention, electrodes positioned on a subject to detect electrophysiologic signals produced thereby are connected via leads and switching devices to signal amplifiers. Each such electrode, lead, switching device, and amplifier combination forms a signal channel. The switching devices are controlled by switching device control signals provided by a system processor. The system processor provides a channel disconnect selection graphical user interface to an operator on an operator display, whereby the operator may indicate selected ones of the signal channels. A channel disconnect user interface is also provided, whereby an operator may indicate in a single action that signals from the electrodes in the channels selected using the channel disconnect selection user interface are to be disconnected from their respective amplifiers. Similarly, signals from the electrodes in the selected channels may be reapplied to their respective amplifiers in a single action using the channel disconnect user interface. When the channel disconnect user interface is selected, the switching devices in the channels selected using the channel disconnect selection user interface are opened, to disconnect the signals provided by the electrodes from the corresponding amplifiers. When the channel disconnect user interface is deselected, the switching devices in the channels selected using the channel disconnect selection user interface are closed, thereby reconnecting the signals provided from the electrodes to the corresponding amplifiers in the selected channels. In channels which are not selected using the channel disconnect selection user interface, the switching devices remain closed when the channel disconnect user interface is selected, such that signals from the electrodes are provided to the corresponding amplifiers in those channels regardless of whether the channel disconnect user interface is selected or not.
An electrode disconnect system in accordance with the present invention may be used to easily disconnect electrode signals from their corresponding amplifiers in a medical signal monitoring system, e.g., before an electrical stimulus is applied to the subject, without requiring physical removal of electrodes from a subject or the physical removal (unplugging) of electrode leads from an amplifier circuit. As discussed above, high voltage electrical stimulus signals applied to a subject may saturate amplifiers connected to electrodes placed on the subject near the point where the stimulation is applied. Before applying such electrical stimulation, the channel disconnect selection user interface may be used to indicate selected channels in which the electrodes should be disconnected from their corresponding amplifiers when the electrical stimulation is provided to the subject. Just before electrical stimulation is provided, the channel disconnect user interface is selected, thereby disconnecting the electrodes selected using the channel disconnect selection user interface from their corresponding amplifiers. For example, in response to selecting the channel disconnect user interface, switching devices connected between the electrodes selected using the channel disconnect selection user interface and inputs to corresponding amplifiers are opened, e.g., via control signals provided to the switching devices by the system processor. At this point, electrical stimulation can be provided to the subject without risk of saturating the amplifiers in the selected signal channels, and without physically removing any electrodes from the subject or electrode leads from an amplifier circuit. After electrical stimulation is complete, the channel disconnect user interface may be simply deselected. In response to deselecting the channel disconnect user interface, the electrodes in the channels selected using the channel disconnect selection user interface are reconnected to the inputs of their corresponding amplifiers by, e.g., closing the switching devices in the selected channels. Thus, an electrode disconnect system and method in accordance with the present invention may be used in combination with a medical signal monitoring system for monitoring various electrophysiologic signals from a subject, to facilitate periodically performing tests requiring the application of electrical stimulation to the subject using such a system, without requiring physically disconnecting electrodes from a subject (or from an amplifier""s input connection box) prior to such testing, to prevent amplifier saturation, and then physically reconnecting the electrodes to a subject (or to the amplifier""s input connection box) after a stimulation test is complete.
In accordance with the present invention, the electrodes in signal channels selected using the channel disconnect selection user interface may be disconnected from and reconnected to their corresponding signal amplifiers, e.g., by opening and closing the switching devices in such channels, either directly in response to the selection and deselection, respectively, of the channel disconnect user interface, or automatically in timed relation to an applied electrical stimulus signal. In the latter case, the channel disconnect user interface, or another user interface, may be used to enable the automatic disconnection and reconnection of the electrodes from their corresponding amplifiers in selected signal channels when an electrical stimulus signal is applied to a subject. When automatic connection and disconnection is enabled, the electrodes in signal channels selected using the channel disconnect selection user interface will be automatically disconnected from their corresponding amplifiers just prior to the application of an electrical stimulus signal to a subject, and automatically reconnected to their corresponding amplifiers following a delay time after delivery of the stimulus signal is complete. Delivery of the electrical stimulus signal and control of switching devices in the selected signal channels to provide such automatic electrode signal disconnection and reconnection may be controlled by the medical monitoring system processor. The time periods between automatic electrode disconnection and the beginning of electrical stimulation and between the end of electrical stimulation and automatic electrode reconnection may be user selectable.
Further objects, features, and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.